A variety of display systems have been devised to present aircraft and flight information, such as pitch and roll attitude, altitude, airspeed, heading, and the like, to the pilot. These display systems typically use a combination of alphanumeric and graphical information to indicate the state of the aircraft on a single display. Two general categories of aircraft display systems commonly found in commercial, military, and civilian aircraft include a panel-mounted variety (e.g., a Head-Down Display or HDD) and a Head-Up Display (HUD) variety.
In general, a greater degree of information may be presented on a panel-mounted aircraft display than a HUD. A HUD typically projects flight information onto a combiner located within the general viewing area (e.g., the cockpit window) of the aircraft pilot, and the amount of flight information provided onto the combiner is generally limited to permit simultaneous viewing of the flight information and the environment seen beyond the cockpit window. Additionally, many conventional HUD systems are monochromatic because some colors provide greater viewing performance than other colors and because multi-colored Cathode Ray Tube (CRT) projectors used in such HUD systems generally process flight information at a rate unsuitable for real-time performance. Without concern for viewing of the environment beyond the cockpit window, panel-mounted aircraft displays generally lack these constraints and can provide multi-colored presentations with greater information detail than conventional HUD displays.
One display instrument presented in these display systems is an Attitude Direction Indicator (ADI). An ADI generally indicates a reference point or line, e.g., a horizon line, relative to the position of an aircraft. The aircraft may be represented by a fixed element of the ADI display, and most ADIs depict the aircraft wings as one or more horizontal marks that are centered with respect to the display screen. The horizon line rendered on the ADI display may move up and down to reflect pitch changes of the aircraft. Similarly, the horizon line may rotate to reflect roll changes of the aircraft.
Some conventional ADIs used in HDDs include a blue colored region above the horizon line (e.g., representing the sky) and a brown or tan colored region below the horizon line (e.g., representing the Earth or ground). This color scheme is particularly useful when the pilot attempts to visually ascertain the relative position of the aircraft (e.g., with respect to the ground) within a short time period because the two colors more clearly distinguish the sky from the ground. While an ADI having such a color scheme may be suitable in many HDDs, most conventional HUDs, such as those employing CRT projectors, lack a multi-colored depiction of the regions above and below the horizon line. Under normal circumstances, a conventional HUD uses a pitch ladder and a roll scale, instead of the conventional ADI, and thus lacks features to distinguish the sky from the ground.
Distinguishing the sky from the ground is particularly useful during the occurrence of an upset condition. An upset condition may occur when the aircraft has an unusual attitude (e.g., an attitude promoting aircraft stall) that requires an eventual recovery from the unusual attitude. When the aircraft is oriented such that either all sky or all ground would be displayed, the conventional ADI used in HDDs presents some of both the sky and ground to minimize the pilot workload in ascertaining which direction to direct the aircraft for recovery.
Accordingly, it is desirable to provide an aircraft HUD system having a display that maintains both a sky region and a ground region and differentiates the sky region from the ground regions within the ADI during an upset condition. In addition, it is desirable to provide a method for displaying an ADI in an aircraft HUD system that maintains both a sky region and a ground region within the ADI and differentiates the sky region from the ground region within the ADI during an upset condition. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.